Airflow conductances

The airflow network (Fig. 11.41 is composed of nodes, interconnected by links, representing individual airflow paths. Internal nodes represent the individual zones of the building, and external nodes represent faqade locations, related to a specific set of wind pressure coefficients. Each link represents a specific airflow conductance type. 

Evaporation is accompanied by local cooling and condensation by local warming. The addition of mas s to droplets and the conduction of latent heat away from the surface of the droplet or particle are, as has been pointed out by Pritchard (1987), the determining processes of particle growth. Under conditions of turbulent airflow, conduction of heat away from the surface of droplets or particles is enhanced and hygroscopic growth rates exceed those found under still conditions or under conditions of laminar airflow. The implications of this will be considered later. 

Experimental studies conducted by Grimitlyn on heated and chilled confined jets showed that the airflow pattern remains the same as for isothermal... 

Similar studies were conducted by Troyanovsky, who concluded that to maintain the airflow pattern in rooms with heated or cooled air supply as in isothermal conditions, it is necessary that the rise of horizontally supplied jet does not exceed Ay = 0.1 BH at the distance from the outlet X = 0.15K BH) -. From this assumption the following equation for the maximum air temperature difference was derived ... 

The terms zonal model and flow element are also used for the simplified characterization of the flow field in a single enclosure. There, a zone represents a partial volume of air in the enclosure, whereas in the multizone models described here, a zone represents a specific enclosure which is connected to other enclosures by air conductances (see The Airflow Network later). 

Airflows are determined basically by a steady-state calculation for each time step. At each time step, first, pressures at external nodes are calculated on the basis of the wind pressure coefficients and the actual wind speed and direction. Then, for all conductances, the local pressures at each side of the link are calculated. At internal links, this pressure is dependent on the (unknown) zone pressure p and the aerostatic pressure variation due to the height of the link with respect to the zone reference height. At external links, this pressure is dependent on the external node pressure and the aerostatic pressure variation due to the height of the link with respect to the stack reference height. For the aerostatic pressure, the air density is determined considering the temperature, the humidity, and (if relevant) the contaminant concentrations in the zone or in the outside air, respectively. From this, the pressure differences across each conductance can be calculated, and from this the mass airflow tor each conductance /. 

In some texts guidance is given to estimate and evaluate the leakage of buildings and building components. The multizone airflow model can also be used to adjust the assumed conductances to an overall building leakage, measured by blower door technique, for example. 

The primary results of multizone airflow calculations are the flows for each conductance. For large openings, the two flows in either direction through the opening are calculated. From this, the following results can be derived (per time step) ... 

An experimental nm had been conducted to study the effect of airflow rate in the 3 litres aeration wastewater treatment tank. Nutrients were added in the treatment tank to ensure sufficient bacterial growth. In each experiment, the cell optical density, COD and die concentration of chemicals equivalent to carbohydrates were monitored for the duration of aeration. 

Further experiments were conducted in a large aeration tank, 15 litres batch system to study die dry weight cell density, COD, carbohydrate, dissolved oxygen and oxygen transfer modelling. Two different airflow rates, 5 and 10 litres/min, were applied. However,... 

The Department of Homeland Security has funded preliminary studies to elaborate specific chemical/biological threat vectors and to increase understanding of airflows in several terminals and boarding areas of San Francisco International Airport and Albuquerque Airport. It has also conducted an exercise in which the many airport decision makers (e.g., in areas of operations, security, fire control and prevention, public health and safety, and environmental is-... 

The airflow equations presented above are based on the assumption that the soil is a spatially homogeneous porous medium with constant intrinsic permeability. However, in most sites, the vadose zone is heterogeneous. For this reason, design calculations are rarely based on previous hydraulic conductivity measurements. One of the objectives of preliminary field testing is to collect data for the reliable estimation of permeability in the contaminated zone. The field tests include measurements of air flow rates at the extraction well, which are combined with the vacuum monitoring data at several distances to obtain a more accurate estimation of air permeability at the particular site. 

Dead space. Anatomical dead space is equal to the volume of the conducting airways. This is determined by the physical characteristics of the lungs because, by definition, these airways do not contain alveoli to participate in gas exchange. Alveolar dead space is the volume of air that enters unperfused alveoli. In other words, these alveoli receive airflow but no blood flow with no blood flow to the alveoli, gas exchange cannot take place. Therefore, alveolar dead space is based on functional considerations rather than anatomical factors. Healthy lungs have little or no alveolar dead space. Various pathological conditions, such as low cardiac output, may result in alveolar dead space. The anatomical dead space combined with the alveolar dead space is referred to as physiological dead space ... 

The prototype design 2 was expected to have similar air seal problems as the prototype 1 therefore the prototype design 3 was constructed and tested, instead. Since all the modification was restricted to the wheel, prototype design 3 allowed us to simply use the existing commercial appliance design. The dehumidifier was first test run under different operating conditions and the airflow, temperature and humidity at different locations within the appliance were measured and recorded. The airflow, temperature and humidity profiles were used to calculate the optimum quantities and distributions of catalysts and adsorbents in the wheel (Fig. 12.8-6). The wheel was replaced in the dehumidifier appliance and tested with sensors inserted at the locations shown in Fig. 12.8-11. The results show that the airflows and temperatures remained within normal operating values. Laboratory and field tests were conducted and the results are reported in the next section. 

Laboratory tests were conducted for airflow, noise, dehumidification and VOC remediation by the prototype. 

Five weeks air survey was conducted to determine the air quality at the clinic. The reception area has a lower bioaerosol loading of 300-800 CFU/m3 owing to better airflow and open floor plan. The doctor s consultation room displays 2-to-3 times higher amount of airborne bioaerosol (i.e., 600-1400 CFU/m3) due to poor air ventilation. The airflow is roughly 0.1 m3/s, giving an overall air... 

Tables 12.9-5 and 12.9-6 summarize the results of the three months period when weekly measurements were conducted. The temperature and humidity of the clinic is relative constant at around 23 °C and 80 %, but the bioaerosol level changes by the hour and day-to-day depending on the number of patients and outside air quality. The Prototype Unit was placed in the doctor s consultation room and the airflow was set at normal-speed (Fig. 12.9-12c), allowing a complete exchange of the room s air every 30 minutes. The air sample from the reception and doctor s consultation room were sampled within 20 minutes of each other. The data in the tables show that the airborne microorganisms in the doctor s consultation room remained higher compared to the reception area. However, this is a significant improvement when compared to the level when the Prototype Unit was not in use. Data obtained by measuring the inlet and outlet bioaerosol in the Prototype Unit indicated that 60 % and 67 % reduction in airborne bacteria and fungi was obtained, respectively. The performance was maintained during the six months test.

Odour measurements in agriculture have been conducted by the Institute of Agricultural Engineering for a number of years. During this time various olfactometers have been used. It was found that the airflow of the olfactometer is one of the major parameters effecting the results. Futhermore frequent calibration of the olfactometers in use is advisable. 

Heavier soils with lower pneumatic conductivities require a significantly more intensive effort to induce airflow and may prove prohibitive to treat with this or similar technologies. 

The ability of currently used aircraft probes to accurately sample aerosols has been questioned. Huebert et al. (8) conducted a comparative study of several different types of aerosol probes, all mounted on the same aircraft. The results suggested that substantial losses of particles occurred in all of the inlet systems. Because of the limited nature of the study, however, the causes of the aerosol losses could not be identified. The results of the Huebert study prompted a workshop to reexamine the entire issue of aerosol sampling from aircraft (9). An important conclusion of the workshop was that currently there is insufficient knowledge to adequately describe important characteristics of airflow and particle trajectories at flight speeds of aerosol sampling probes used on aircraft. 

The difference %i Xo in concentration of a vapour or aerosol in the free stream and at a surface is the driving force for deposition. Since the ratio Q/(x 1 — Xo) has the dimensions of a velocity, it is called the velocity of deposition, denoted vg. Alternatively, on the electrical analogy, vg is the conductance and its reciprocal, r is the resistance to mass transfer. If the boundary layer of an airflow over a surface has two or more parts, for example above and below the top of the roughness elements, the resistances of these layers are additive, since... 

Foam fractionation is a promising technique for concentrating proteins because of its simplicity and low operating cost. One such protein that can be foamed is the enzyme cellulase. The use of inexpensively purified cellulase may be a key step in the economical production of ethanol from biomass. We conducted foam fractionation experiments at total reflux using the cellulase component P-glucosidase to study how continuous shear affects P-glu-cosidase in a foam such as a fermentation or foam fractionation process. The experiments were conducted at pH 2.4, 5.4, and 11.6 and airflow rates of 3,... 

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